Soil is the foundation of our food supply. It stores water, carbon and nutrients and is home to a large share of the world’s biodiversity. More than half of global biodiversity is estimated to live below ground. Yet biodiversity, and with it soil health, is declining worldwide, with consequences for agriculture, food security and the functioning of entire ecosystems.
In 2021, researchers from the University of Zurich (UZH) and Agroscope, the Swiss federal center of excellence for agricultural research, launched the citizen science project Proof by Underpants (Beweisstück Unterhose) to draw attention to this often overlooked ecosystem and also collect scientific data. Following a standardized procedure, 1,000 volunteers buried more than 2,000 pairs of cotton underwear and 12,000 tea bags at around 1,000 locations across Switzerland. Two months later, they dug them up, photographed them and sent them to the laboratory together with a soil sample for further analysis.
Decomposition rate as indicator of soil life
The results, a map of soil activity, have now been published in the journal Plants, People, Planet. The analysis shows that the underwear decomposed at very different rates depending on the location, with the decomposition rate providing a measure of biological activity: the more active the soil organisms, the faster they break down the cotton material.
The underwear decomposed most rapidly in private gardens, where the researchers found the highest levels of organic matter – ideal conditions for earthworms, fungi, bacteria and other soil-dwelling organisms. Soil organisms were least active in lawns, while agricultural fields and meadows fell somewhere in between.
Land use is the key factor
“Our results show that how soil is managed can significantly affect both soil life and soil quality,” says co-study leader Marcel van der Heijden, UZH professor of agroecology. “Healthy, biologically active soil is crucial for fertility, nutrient cycling and many other ecosystem services.” Measures that can promote soil life include keeping the soil permanently covered, adding compost, diversifying crop rotations and limiting the use of mineral fertilizers and pesticides.
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Land use proved to be the most important factor influencing how quickly the underwear decomposed. Whether a site was used as a garden, meadow, cultivated field or lawn explained the differences better than most of the soil properties measured. Chemical soil characteristics, such as nutrient levels, also played a significant role.
Some soils oversupplied with nutrients
The results also show that rapid decomposition of the underwear often indicates high soil fertility and a good supply of nutrients. This is particularly beneficial for agricultural production. “However, maximum decomposition is not desirable in every ecosystem,” says co-project leader Franz Bender, head of the agroecological assessments team at Agroscope.
“In near-natural habitats such as forests, very high nutrient levels can indicate disruptions to the natural balance of nutrients. In gardens, too, rapid decomposition of the underwear may point to an oversupply of nutrients,” says Bender. In these cases, it may be worth checking whether fertilizer use should be reduced. Soil life also depends strongly on temperature and soil moisture; if conditions are too cold or too dry, the soil is barely active.
Raising awareness of soil health
Burying cotton underwear can provide a simple yet meaningful way to reveal differences in biological activity and soil fertility. The researchers therefore propose an “underwear index” as an easy-to-understand way of illustrating soil processes and raising public awareness of the need to protect soils.
Journal Reference:
Bender, S. F., Bürge, D., Bragazza, L., Knop, E., Masson, S., Peter, N., Demarmels, R., Mueller, D., Imhof, A., Viviani, P., Bieri, A., Liebisch, F., Geisen, S., Hautier, Y., Panagos, P., Garcia-Palacios, P., Goberna, M., Johnson, D., Jöhr, S., … van der Heijden, M. G. A., ‘Soil health assessment using buried cotton underpants with the help of 1000 citizen scientists’, Plants, People, Planet online ver., 1–19 (2026). DOI: 10.1002/ppp3.70259
Article Source:
Press Release/Material by University of Zürich (UZH)
Featured image credit: Priska Koller | Agroscope
